For the production and processing of granules, different processes are necessary. An apparatus often used for such processes is the so-called fluid-bed apparatus described, for instance, in DE-09 27 38 485. In such an apparatus, the lower end of the fluid-bed container, which has a sieve bottom, is provided with a horizontal rotor-disk. Beneath the sieve bottom there is a wind chamber. In order to adjust the apparatus to different kinds of granules, the lower part of the container surrounding the rotor-disk can, according to DE-PS 28 05 397, have a conical shape and the rotor-disk can be adjustable in height, whereby the size of a ring-slit provided between the rotor-disk and the surrounding cylindrical wall of the fluid-bed container can be varied to thereby regulate the strength of the air stream.
Apparatus of the kind described above have various disadvantages. For instance, in order to precisely regulate the slit between the container wall and the rotor-disk, the requirements to the container geometry--especially in the lower, conically formed part--are very high. Also, problems arise during the practical usage of such an apparatus. For example, the circulating movement of the solid materials caused by such an apparatus, which is referred to hereafter as the "annular movement", is important for a good mixture and regular processing of the granules. Such annular movement is produced primarily by the centrifugal forces exerted by the rotor-disk on the granules. Should, for instance, the drying performance be increased, then the airstream flowing through the fluid-bed cannot be arbitrarily intensified because when the airstream reaches a certain intensity, the annular movement of the granules is disturbed and proper drying cannot be achieved. Moreover, when a high intensity airstream is used in connection with a coating and drying process, a powder feeding operation or an atomizing operation in accordance with the so-called ultrasonic principle is impeded if not made impossible because the fine dust of the atomizing operation and the liquid mist of the atomizing operation are carried away by the airstream and thus are not at the disposal of the particles which are being coated and dried.